Astrocytic processes form the surface of the mammalian brain and entirely surround all blood vessels in the brain. One approach to understanding the function of these astrocytic processes is to examine the biochemical characteristics and function of a specific membrane-associated protein which is highly concentrated in their membranes. This protein, which has been termed "assemblies" from its appearance in freeze-fractured tissue, is of further interest in that it undergoes a unique conformational change within seconds of circulatory arrest. It is possible that this conformational change alters astrocytic membrane permeability, causing the astrocytic swelling which complicates ischemic brain injury. Tissues culture methods have been devised which elicit the differentiation of assemblies in primary astrocytes, and serum factors which influence astrocyte lineage and differentiation are under study. Cultures are being used to examine more precisely the etiology of the conformational change that follows circulatory arreest. In preliminary experiments, a band in electrophoretic gels has been identified which is correlated with the presence of assemblies, and which will be used as one approach to the generation of monoclonal antibodies. Such antibodies will serve to facilitate biochemical characteization of the assembly protein, and can be used to develop a quantitative assay for it that will greatly simplify studies of astrocyte development and lineage. Monoclonal and polyclonal antibodies may also serve as probes for the function of the protein. As we learn about this property of astrocytes, we may be able to design better responses to the clinical problems of astrocytic swelling in ischemic and traumatic injury.